A. Field of the Invention
The present invention relates to the field of illuminating systems, and more particularly to the field of display devices used in automotive lighting.
B. Description of Related Art
Center high mount stop lights (CHMSL) are red colored, light emitting display devices that are mounted to illuminate to the rear of an automobile from a position that is elevated and roughly center to the stop lights on the right and left sides of the rear end of the automobile. Conventional CHMSLs consist of a lamp assembly having a housing containing an external lens with a bulb. The housing typically has a reflective coating on the inside surface. The lamp assembly may come in various shapes and sizes. Many of these assemblies require several components to be connected together. For example, in addition to the lens and housing, a separate bracket may be included to facilitate the attachment of a bulb socket. The complexity of the structure of CHMSLs may add significantly to the cost of manufacturing the CHMSLs. This in turn adds to the cost of the automobile.
CHMSLs may be mounted in any part of the rear of the automobile that allows the CHMSL to be elevated and centered relative to the low-mounted brake lights. Because of its elevated position, the visibility of CHMSLs may be improved by designing it to illuminate with a high-intensity beam having a light spread distribution in the vertical direction that facilitates visibility from different elevations. Manufacturers are now required to produce CMHSLs having a light spread distribution in accordance with specifications set by government regulations, such as for example, the FMVSS 571.108 issued by the National Highway Traffic Safety Administration.
The use of light guides for exterior lighting is known in the art. U.S. Pat. No. 5,772,304 to Smith (hereinafter "Smith") discloses a rear exterior lamp that uses a light guide in which a three dimensional tapered surface reflects light through a light panel. One disadvantage of using Smith, particularly for use as a CHMSL, is that the light emitted by the light panel having the tapered surface does not diverge to provide a light spread distribution. The light emitted by Smith is substantially parallel making it unsuitable for use as a CHMSL or any other exterior lighting requiring a light spread distribution. Smith also requires a light panel and other parts that result in a structure that significantly complex making it a costly solution in terms of labor and material.
U.S. patent application Ser. No. 5,165,772 to Wu (hereinafter "Wu") discloses a visual display device structure using a light guide that is particularly designed for use as a CHMSL. The device in Wu includes a substrate material that is stepped on one surface, each step being at an angle to provide a light distribution spread using the light diverging through refraction at the step. One disadvantage with using Wu, however, is that its use is limited to CHMSLs that are mounted at small angles. Another disadvantage with Wu is that the stepped surface makes the light guide in Wu unsuitable for use as exterior lighting.
One of ordinary skill in the art will appreciate that while the present discussion focuses on CHMSLs, the principles, problems and solutions may also apply to other lighting systems. For example, it may be desirable in other lighting applications such as tail lights, other signal lights for automobiles, street lights, interior lighting, courtesy lighting and other signal lighting to illuminate at a selected light spread distribution.
It would be desirable to have an exterior lighting system that may be made to provide a high-intensity beam with a selected light spread distribution.
It would also be desirable to provide an exterior light with a simple structure that may be manufactured at a low cost. For example, it would be desirable to have an exterior light that uses no external lens.
It would also be desirable to provide an external lighting system that is flexible in design to permit a variety of configurations and unique appearance.